RAIS Risk Exposure Models for Radionuclides User's Guide

Note

The RAIS presents this updated Risk calculator in response to the following: incorporating chemical-specific parameters from the lastest EPI release, addition of air as a media, and conversion to a new database structure. The previous RAIS Risk calculator presented Risks for radionuclides and chemcials together. Recent development of chemical and radionuclide exposure equations has necessitated that the RAIS separate the chemicals and the radionuclides. To calculate risks for chemicals, use the RAIS Risk Exposure Models for Chemicals calculator.

Currently the agricultural equations for the RAIS chemical and radionuclide risk calculators are identical. The EPA's Preliminary Remediation Goals for Radionuclide Calculator offers more biota choices but with a different plant/soil/water uptake method. The EPA's resident soil equation includes ingestion of produce and the RAIS radionuclide equation does not to be consistent with the chemcial risk equation.

The purpose of this calculator is to assist Remedial Project Managers (RPMs), On Scene Coordinators (OSC’s), risk assessors and others involved in decision-making at hazardous waste sites and to determine whether levels of contamination found at the site may warrant further investigation or site cleanup, or whether no further investigation or action may be required.

The risk values presented on this site are radionuclide-specific values for individual contaminants in air, water, soil and biota that may warrant further investigation or site cleanup.

This portion of the risk assessment process is generally referred to as "Risk Characterization". This step incorporates the outcome of the previous activities and calculates the risk or hazard resulting from potential exposure to radionuclides via the pathways and routes of exposure determined appropriate for the source area.

The linear risk equation, listed above, are valid only at low risk levels (below estimated risks of 0.01). For sites where radiological exposure might be high (estimated risks above 0.01, an alternate calculation should be used. The one-hit equation, which is consistent with the linear low-dose model, should be used instead (RAGS, part A, ch. 8). The results presented on the RAIS use this rule. In the following instances, one-hit rule is used independently in our risk output tables:

Risk from a single exposure route for a single radionuclide.

Summation of single radionuclide risk (without one-hit rule applied to single radionuclide results) for multiple exposure routes (right of each row).

Summation of risk (without one-hit rule applied to single radionuclide results) from a single exposure route for multiple radionuclides (bottom of each column).

Risks are based on default exposure parameters and factors that represent Reasonable Maximum Exposure (RME) conditions for long-term/chronic exposures and are based on the methods outlined in EPA’s Risk Assessment Guidance for Superfund, Part B Manual (1991) and Soil Screening Guidance documents (1996 and 2002).

Site-specific information may warrant modifying the default parameters in the equations and calculating site-specific risks. In completing such calculations, the user should answer some fundamental questions about the site. For example, information is needed on the contaminants detected at the site, the land use, impacted media and the likely pathways for human exposure.

Whether these generic risks or site-specific risks are used, it is important to clearly demonstrate the equations and exposure parameters used in deriving risks at a site. A discussion of the assumptions used in the risk calculations should be included in the decision document for a CERCLA site.

EPA classifies all radionuclides as Group A carcinogens ("carcinogenic to humans"). Group A classification is used only when there is sufficient evidence from epidemiologic studies to support a causal association between exposure to the agents and cancer. The appendix radionuclide table, from the Center for Radiation Protection Knowledge, lists ingestion, inhalation and external exposure cancer slope factors (risk coefficients for total cancer morbidity) for radionuclides in conventional units of picocuries (pCi). Ingestion and inhalation slope factors are central estimates in a linear model of the age-averaged, lifetime attributable radiation cancer incidence (fatal and nonfatal cancer) risk per unit of activity inhaled or ingested, expressed as risk/pCi. External exposure slope factors are central estimates of lifetime attributable radiation cancer incidence risk for each year of exposure to external radiation from photon-emitting radionuclides distributed uniformly in a thick layer of soil, and are expressed as risk/yr per pCi/gram soil. External exposure slope factors can also be used which have units of risk/yr per pCi/cm2 soil. When combined with site-specific media concentration data and appropriate exposure assumptions, slope factors can be used to estimate lifetime cancer risks to members of the general population due to radionuclide exposures. EPA currently provides guidance on inhalation risk assessment in RAGS Part F (Risk Assessment Guidance for Superfund Volume I: Human Health Evaluation Manual (Part F, Supplemental Guidance for Inhalation Risk Assessment). This guidance only addresses chemicals. The development of inhalation slope factors for radionuclides differs from the guidance presented in RAGS Part F for development of inhalation unit risk (IUR) values for chemicals.

The SFs from the Center for Radiation Protection Knowledge differ from the values presented in HEAST. The SFs were calculated using ORNL's DCAL software in the manner of Federal Guidance Report 12 and 13. The radionuclides presented are those provided in the International Commission on Radiological Protection (ICRP) Publication 107. This document contains a revised database of nuclear decay data (energies and intensities of emitted radiations, physical half-lives and decay modes) for 1,252 naturally occurring and manmade radionuclides. ICRP Publication 107 supersedes the previous database, ICRP Publication 38 published in 1983. In addition to radionuclides in ICRP Publication 107, the assembled data files or tables contain entries that include the contribution of daughter products in secular equilibrium with their longer-lived parents. These entries are identified by the addition of "+D" and to the nuclide name where "+D" refers to a 100 year period of progeny ingrowth.

Several of the isotopes are listed with a '+D' designation. This designation indicates that the slope factor includes the contribution from ingrowth of daughter isotopes out to 100 years. The intention of this designation is to make realistic risks by including the contributions from their short-lived decay products. The +D designation indicates that the parent radionuclide is accompanied by its progeny. In general, the activity of chain members assumes progeny ingrowth of 100 years. There is one exception for the inhalation slope factor for Rn-222+D. EPA assumes a 50% equilibrium value for radon decay products (Po-218, Pb-214, Bi-214 and Po-214) in air. Before applying risks to a site, it should be determined if the isotopes present are in secular equilibrium. If the isotopes are found to be in secular equilibrium, the +D risks should be used for the parent isotope and the daughters included in the +D can be ignored. If the isotopes are not in secular equilibrium, risks should be applied individually for each daughter isotope. However, in the absence of empirical data, the "+D" values for radionuclides should be used unless there are compelling reasons not to.

For example, if analytical data from a site reveal that Ra-226, Rn-222 and Po-218 are detected at a site and that they are in secular equilibrium, the risk for Ra-226+D should be applied and the Rn-222 and Po-218 can be ignored.

Another example could concern a decay chain in secular equilibrium like Th-228. Even though the decay chain for Th-228 is long, there is no Th-228+D slope factor because the activity of any of the progeny after 100 years of chain ingrowth was less than 90% of the parent's activity. The general rule for non-branching chains is, if a parent has any progeny with greater than 90% of the parent's activity at 100 years, a +D is calculated. For branching chains, if any branch contributes over 90% of the branch fraction activity, at 100 years, a +D is calculated. An example of this would be Cs-137+D where the branching fraction is 94.4 % to Ba-137m and at 100 years Ba-137m contributes over 90% of the activity than the parent, Cs-137. In either chain type, if the total dose contribution of the progeny is insignificant relative to the parent's contribution, then no +D values are calculated.

In this case of Th-228, the risks for Th-228, Ra-224+D, Po-216, Pb-212, Bi-212+D and Tl-208 should be used. If no part of the decay chain is in secular equilibrium, the user should use each of the risks for isotopes in the decay chain that have slope factors (e.g., Ra-224, Rn-220, Po-216, Pb-212, Bi-212, Po-212, and Tl-208). If part of the decay chain is in secular equilibrium, then the user may use that particular +D slope factor that covers that part of the decay chain, while using the slope factors for the other radionuclides.

Selected radionuclides and radioactive decay chain products are designated with the suffix "+D" to indicate that cancer risk estimates for these radionuclides include the contributions from their short-lived decay products, assuming equal activity concentrations (i.e., secular equilibrium) with the principal or parent nuclide in the environment. For all radionuclides without the "+D" suffix, only intake or external exposure to the single radionuclide is considered. Most radionuclides with a +D designation include the entire decay chain to the stable terminal nuclide in the slope factors. The Center for Radiation Protection Knowledge provides a table of the 100 year progeny ingrowth for the isotopes in Table 2 of Appendix A of Calculations of Slope Factors and Dose Coefficients. This table provides the associated decay chain used in the slope factors. This table is reproduced below for common isotopes with the terminal nuclide added.

Most dose and risk coefficients are presented for radionuclides in their ground state. In the decay process, the newly formed nucleus may be in an excited state and emit radiation; e.g., gamma rays, to lose the energy of the state. The excited nucleus is said to be in a metastable state which is denoted by the chemical symbol and atomic number appended by "m"; e.g., Ba-137m. If additional higher energy metastable states are present then "n", "p", ... is appended. Metastable states have different physical half-lives and emit different radiations and thus unique dose and risk coefficients. In decay data tabulations of ICRP 107), if the half-life of a metastable state was less than 1 minute then the radiations emitted in de-excitation are included with those of the parent radionuclide. Click to see a graphical representation of the decay of Cs-137 to Ba-137.

Eu-152, in
addition to its ground state has two metastable states: Eu-152m and
Eu-152n. The half-lives of Eu-152, Eu-152m and Eu-152n are: 13.5 y, 9.31
m and 96 m, respectively and the energy emitted per decay is 1.30 MeV, 0.080 MeV, and 0.14 MeV, respectively.

NCRP 123 (NCRP). NCRP Report No. 123, Screening Models for Releases of Radionuclides to the Atmosphere, Surface Water, and Ground. National Council on Radiation Protection and Measurements. January 22, 1996. Spreadsheet of values.

Fish bioconcentration factor (BCF (L/kg). IAEA, RESRAD. BCF is the ratio of the radionuclide concentration in the fish tissue (pCi/kg fresh weight) from all exposure pathways relative to that in water (pCi/L).

Soil to water partition coefficient (Kd (mg/kg-soil per mg/L water or simplified = L/kg). EPAKD, IAEA, SSL, RESRAD, BAES. (Kd is the ratio of the mass activity density (pCi/kg) of the specified solid phase (usually on a dry mass basis) to the volumetric activity density (Bq/L) of the specified liquid phase.

Soil to plant transfer factor-wet (Bvwet (pCi/g plant per pCi/g soil). IAEA, NCRP, SSL, RESRAD, BAES. The values for cereal grain are used from IAEA. (Bvwet is the ratio of the activity concentration of radionuclide in the plant (pCi/kg wet mass) to that in the soil (pCi/kg dry mass). Note: Some Bvwet values were derived from Bvdry sources, assuming the ratio of dry mass to fresh mass was presented in the source documents.

Soil to plant transfer factor-dry (Bvdry (pCi/g plant per pCi/g soil). IAEA, NCRP, SSL, RESRAD, BAES. The values for cereal grain are used. (Bvdry is the ratio of the activity concentration of radionuclide in the plant (pCi/kg dry mass) to that in the soil (pCi/kg dry mass). Note: Some Bvdry values were derived from Bvwet sources, assuming the ratio of dry mass to fresh mass was presented in the source documents.

When using risks, the exposure pathways of concern and site conditions should match those taken into account by the screening levels. (Note, however, that future uses may not match current uses. Future uses of a site should be logical as conditions which might occur at the site in the future.) Thus, it is necessary to develop a conceptual site model (CSM) to identify likely contaminant source areas, exposure pathways, and potential receptors. This information can be used to determine the applicability of screening levels at the site and the need for additional information. The final CSM diagram represents linkages among contaminant sources, release mechanisms, exposure pathways, and routes and receptors based on historical information. It summarizes the understanding of the contamination problem. A separate CSM for ecological receptors can be useful. Part 2 and Attachment A of the Soil Screening Guidance for Radionuclides: Users Guide (EPA 2000a) contains the steps for developing a CSM.

As a final check, the CSM should answer the following questions:

Are there potential ecological concerns?

Is there potential for land use other than those listed in the risk calculator (i.e. , residential and industrial)?

Are there other likely human exposure pathways that were not considered in development of the risks?

Are there unusual site conditions (e.g. large areas of contamination, high fugitive dust levels, potential for indoor air contamination)?

The risks may need to be adjusted to reflect the answers to these questions.

Natural background radiation should be considered prior to applying risks as cleanup levels. Background and site-related levels of radiation will be addressed as they are for other contaminants at CERCLA sites. For further information, see EPA's guidance "Role of Background in the CERCLA Cleanup Program", April 2002, (OSWER 9285.6-07P). It should be noted that certain ARARs specifically address how to factor background into cleanup levels. For example, some radiation ARAR levels are established as increments above background concentrations. In these circumstances, background should be addressed in the manner prescribed by the ARAR.

As with any risk based tool, the potential exists for misapplication. In most cases, this results from not understanding the intended use of the risks. In order to prevent misuse of the risks, the following should be avoided:

Applying risk levels to a site without adequately developing a conceptual site model that identifies relevant exposure pathways and exposure scenarios.

Use of risk levels as cleanup levels without the consideration of other relevant criteria such as ARARs.

Use of risk levels as cleanup levels without verifying numbers with a health physicist/risk assessor.

Use of outdated risk levels tables that have been superseded by more recent publications.

The chronic daily intake (CDI) equations consider human exposure to individual contaminants in air, water, soil, sediment and biota. The technical discussion is aimed at producing risk results. The following text presents the land use equations and their exposure routes. The tables at the end of the users guide present the definitions of the variables and their default values. Any alternative values or assumptions used in developing risks on a site should be presented with supporting rationale in the decision documents.

The risk equations have evolved over time and are a combination of the following guidance documents:

This receptor spends most, if not all, of the day at home except for the hours spent at work. The activities for this receptor involve typical home making chores (cooking, cleaning and laundering) as well as gardening. The resident is assumed to be exposed to contaminants via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust and consumption of home grown produce (100% of fruit and vegetables). Adults and children exhibit different ingestion rates for soil and produce. For example the child resident is assumed to ingest 200 mg per day while the adult ingests 100 mg per day. To take into account the different intake rate for children and adults, age adjusted intake equations were developed to account for changes in intake as the receptor ages.

This receptor spends most, if not all, of the day at home except for the hours spent at work. The activities for this receptor involve typical home making chores (cooking, cleaning and laundering) as well as gardening.

This analysis is designed to look at external exposure from contamination of different area sizes. Areas considered are 1 to 1,000,000 square meters. Isotope-specific area correction factor (ACF) were developed for this analysis.

This receptor spends most, if not all, of the day at home except for the hours spent at work. The activities for this receptor involve typical home making chores (cooking, cleaning and laundering) as well as gardening. The resident is assumed to be exposed to contaminants via the following pathways: inhalation of ambient air and external radiation from contaminants in ambient air. To take into account the different inhalation rates for children and adults, age-adjusted intake equations were developed to account for changes in intake as the receptor ages.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

This receptor is exposed to radionuclides that are delivered into a residence. Ingestion of drinking water is an appropriate pathway for all radionuclides. Activities such as showering, laundering, and dish washing also contribute to inhalation. The inhalation exposure route is only calculated for C-14, H-3, Ra-224, Ra-226, Rn-220, and Rn-222 which volatilize. External exposure to immersion in tapwater and exposure to produce irrigated with contaminated tapwater are also considered.

The risk from consumption of fish is represented here. This is unlike the farmer scenario where the risk is calculated for soil levels protective of fish consumption. Further the ingestion rate is not age adjusted like the farmer scenario.

The soil to groundwater media uses the same water concentration determination equations for resident and indoor worker based on the respective soil concentration entered by the user for each land use. The graphical representation below illustrates the transport of contaminants from soil to groundwater for the resident land use. For more information about soil to groundwater, including equation images, please see section 4.9 of this user guide.

This receptor spends most, if not all, of the workday indoors. Thus, an indoor worker has no direct contact with outdoor soils. This worker may, however, be exposed to contaminants through ingestion of contaminated soils that have been incorporated into indoor dust, external radiation from contaminants in soil, and the inhalation of contaminants present in indoor air. Risks calculated for this receptor are for both workers engaged in low intensity activities such as office work and those engaged in more strenuous activity (e.g., factory or warehouse workers).

This receptor spends most, if not all, of the workday indoors. Thus, an indoor worker has no direct contact with outdoor soils. A gamma shielding factor is applied for this scenario to account for shielding provided by floors and foundation slabs.

This analysis is designed to look at external exposure from contamination of different area sizes. Areas considered are 1 to 1,000,000 square meters. Isotope-specific area correction factor (ACF) were developed for this analysis.

This is a long-term receptor exposed during the work day who is a full time employee working on-site who spends most, if not all, of the workday indoors. The indoor worker is assumed to be exposed to contaminants via the following pathways: inhalation of ambient air and external radiation from contaminants in ambient air.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

This receptor spends most, if not all, of the workday indoors. This worker may be exposed to contaminants in tapwater water. The worker may drink the water, take a shower, and inhale water vapors while showering or as part of industrial operations. Risks calculated for this receptor are for both workers engaged in low intensity activities such as office work and those engaged in more strenuous activity (e.g., factory or warehouse workers).

The indoor worker tapwater land use equation, presented here, contains the following exposure routes:

The soil to groundwater media uses the same water concentration determination equations for resident and indoor worker based on the respective soil concentration entered by the user for each land use. The graphical representation below illustrates the transport of contaminants from soil to groundwater for the indoor worker land use. For more information about soil to groundwater, including equation images, please see section 4.9 of this user guide.

This is a long-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., moderate digging, landscaping) typically involve on-site exposures to surface soils. The outdoor worker is expected to have an elevated soil ingestion rate (100 mg per day) and is assumed to be exposed to contaminants via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust. The outdoor worker receives more exposure than the indoor worker under commercial/industrial conditions.

This is a long-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., moderate digging, landscaping) typically involve on-site exposures to surface soils.

This analysis is designed to look at external exposure from contamination of different area sizes. Areas considered are 1 to 1,000,000 square meters. Isotope-specific area correction factor (ACF) were developed for this analysis.

This is a long-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., moderate digging, landscaping) typically involve on-site exposures to surface soils. The outdoor worker is assumed to be exposed to contaminants via the following pathways: inhalation of ambient air and external radiation from contaminants in ambient air.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

This is a long-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., moderate digging, landscaping) typically involve on-site exposures to surface soils. The composite worker is expected to have an elevated soil ingestion rate (100 mg per day) and is assumed to be exposed to contaminants via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust . The composite worker combines the most protective exposure assumptions of the outdoor and indoor workers. The only difference between the outdoor worker and the composite worker is that the composite worker uses the more protective exposure frequency of 250 days/year from the indoor worker scenario.

This is a long-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., moderate digging, landscaping) typically involve on-site exposures to surface soils.

This analysis is designed to look at external exposure from contamination of different area sizes. Areas considered are 1 to 1,000,000 square meters. Isotope-specific area correction factor (ACF) were developed for this analysis.

This is a long-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., moderate digging, landscaping) typically involve on-site exposures to surface soils. The composite worker is assumed to be exposed to contaminants via the following pathways: inhalation of ambient air and external radiation from contaminants in ambient air. The composite worker combines the most protective exposure assumptions of the outdoor and indoor workers. The only difference between the outdoor worker and the composite worker is that the composite worker uses the more protective exposure frequency of 250 days/year from the indoor worker scenario.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

The excavation worker soil land use has been historically presented on the RAIS and despite the addition of the more recent construction worker scenarios in the following sections, the land use is presented for verification of previous risk assessments.

This is a short-term receptor exposed during the work day. The activities for this receptor (e.g., trenching, excavating) typically involve on-site exposures to surface soils. The excavation worker is expected to have an elevated soil ingestion rate (330 mg per day) and is assumed to be exposed to contaminants via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust. The only difference between the excavation worker and the constriction worker described in section 4.6 is that the excavation worker uses a wind-driven PEF.

This is a short-term receptor exposed during the work day during heavy construction activities outdoors. The activities for this receptor (e.g., trenching, excavating) typically involve on-site exposures to surface soils. The construction worker is assumed to be exposed to contaminants via the following pathways: inhalation of ambient air and external radiation from contaminants in ambient air.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

This is a short-term receptor exposed during the work day working around vehicles suspending dust in the air. The activities for this receptor (e.g., trenching, excavating) typically involve on-site exposures to surface soils. The construction worker is expected to have an elevated soil ingestion rate (330 mg per day) and is assumed to be exposed to contaminants via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust. The only difference between this construction worker and the one described in section 4.12 is that this construction worker uses a different PEF.

The construction worker land use is described in the supplemental soil screening guidance. This land use is limited to an exposure duration of 1 year and is thus, subchronic. Other unique aspects of this scenario are that the PEF is based on mechanical disturbance of the soil. Two types of mechanical soil disturbance are addressed: standard vehicle traffic (e.g., trenching, excavating) and other than standard vehicle traffic (e.g. wind, grading, dozing, tilling and excavating). In general, the intakes and contact rates are all greater than the outdoor worker. Exhibit 5-1 in the supplemental soil screening guidance presents the exposure parameters.

This is a short-term receptor exposed during the work day working around heavy vehicles suspending dust in the air. The activities for this receptor (e.g., dozing, grading, tilling, dumping, excavating) typically involve on-site exposures to surface soils. The construction worker is expected to have an elevated soil ingestion rate (330 mg per day) and is assumed to be exposed to contaminants via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust. The only difference between this construction worker and the one described in section 4.6.1 is that this construction worker uses a different PEF.

The construction land use is described in the supplemental soil screening guidance. This land use is limited to an exposure duration of 1 year and is thus, subchronic. Other unique aspects of this scenario are that the PEF is based on mechanical disturbance of the soil. Two types of mechanical soil disturbance are addressed: standard vehicle traffic (e.g., trenching, excavating) and other than standard vehicle traffic (e.g. wind, grading, dozing, tilling and excavating). In general, the intakes and contact rates are all greater than the outdoor worker. Exhibit 5-1 in the supplemental soil screening guidance presents the exposure parameters.

This is a short-term receptor exposed during the work day who is a full time employee working on-site and who spends most of the workday conducting maintenance activities outdoors. The activities for this receptor (e.g., trenching, excavating, wind, grading, dozing, and tilling) typically involve on-site exposures to surface soils.

This analysis is designed to look at external exposure from contamination of different area sizes. Areas considered are 1 to 1,000,000 square meters. Isotope-specific area correction factor (ACF) were developed for this analysis.

This is a short-term receptor exposed during the work day during heavy construction activities outdoors. The activities for this receptor (e.g., trenching, excavating, wind, grading, dozing, and tilling) typically involve on-site exposures to surface soils. The construction worker is assumed to be exposed to contaminants via the following pathways: inhalation of ambient air and external radiation from contaminants in ambient air.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

This receptor spends time outside involved in recreational activities.

This analysis is designed to look at external exposure from contamination of different area sizes. Areas considered are 1 to 1,000,000 square meters. Isotope-specific area correction factors (ACF) were developed for this analysis.

Two ambient air exposure conditions are offered for this scenario. The first scenario includes a half-life decay function and the second scenario does not. In situations where the contaminant in the air is not being replenished (e.g., an accidental one-time air release from a factory), equations for the first scenario should be used. In situations where the contaminant in the air has a continual source (e.g., indoor radon from radium in the soil, or an operating factory or landfill cap), equations for the second scenario should be used.

This receptor is exposed to radionuclides that are present in surface water. Ingestion of water and immersion in water are appropriate pathways for all radionuclides. Inhalation is not considered due to mixing with outdoor air.

The farmer scenario should be considered an extension of the resident scenario and evaluate consumption of farm products for a subsistence farmer. Like the resident, the farmer assumes the receptor will be exposed via the consumption of home grown produce (100% of fruit and vegetables are from the farm). In addition to produce, 100% of consumption of the following are also considered to be from the farm: beef, milk, fish, swine, egg and poultry. All feed (100%) for farm products is considered to have been grown on contaminated portions of the site. For these farm products, risks are provided for the farm product itself (produce, beef, milk, etc.). Also like the resident, age-adjusted intake equations were developed for all of the consumption equations to account for changes in intake as the receptor ages.

Agricultural Biota, Soil and Water Graphic and Supporting Text

consumption of produce. The exposed and root vegetable consumption rates were combined to represent total vegetable consumption.
Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11.

consumption of poultry. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of eggs. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of beef. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of milk. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. No adjustment for losses U.S. EPA 1998. Home produced dairy total was converted to fluid milk by a factor of 82% (82% of total dairy consumed is fluid milk. )

consumption of swine. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of fish. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss as was done in U.S. EPA 1998.

The farmer scenario should be considered an extension of the resident scenario and evaluate consumption of farm products for a subsistence farmer. Like the resident, the farmer scenario assumes the receptor will be exposed via the following pathways: incidental ingestion of soil, external radiation from contaminants in soil, inhalation of fugitive dust and consumption of home grown produce (100% of fruit and vegetables are from the farm). In addition to produce, 100% of consumption of the following are also considered to be from the farm: beef, milk, fish, swine, egg and poultry. All feed (100%) for farm products is considered to have been grown on contaminated portions of the site. For these farm products, risks are provided for soil which may contribute contaminants to the products. Also like the resident, age-adjusted intake equations were developed for all of the ingestion/consumption equations to account for changes in intake as the receptor ages.

consumption of produce. The exposed and root vegetable consumption rates were combined to represent total vegetable consumption.
Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11.

consumption of eggs. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of poultry. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of fish. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss as was done in U.S. EPA 1998.

consumption of beef. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of milk. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. No adjustment for losses U.S. EPA 1998. Home produced dairy total was converted to fluid milk by a factor of 82% (82% of total dairy consumed is fluid milk. )

consumption of swine. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

The farmer scenario should be considered an extension of the resident scenario and evaluate consumption of farm products for a subsistence farmer. Like the resident, the farmer scenario assumes the receptor will be exposed via the following pathways: ingestion of tapwater, external radiation from contaminants in tapwater, inhalation of gases in tapwater and consumption of home grown produce (100% of fruit and vegetables are from the farm). The inhalation exposure route is only calculated for C-14, H-3, Ra-224, and Ra-226 which volatilize. In addition to produce, 100% of consumption of the following are also considered to be from the farm: beef, milk, fish, swine, egg and poultry. All water (100%) for farm products is considered to have been provided from contaminated portions of the site. For these farm products, risks are provided for the water which may contribute contaminants to the products. Also like the resident, age-adjusted intake equations were developed for all of the ingestion/consumption equations to account for changes in intake as the receptor ages.

consumption of produce. The exposed and root vegetable consumption rates were combined to represent total vegetable consumption.
Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11.

consumption of eggs. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of poultry. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of fish. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss as was done in U.S. EPA 1998.

consumption of beef. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

consumption of milk. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. No adjustment for losses U.S. EPA 1998. Home produced dairy total was converted to fluid milk by a factor of 82% (82% of total dairy consumed is fluid milk. )

consumption of swine. Intake rates from the Exposure Factors Handbook were averaged over age groups to determine adult and child intake rates. Where no intake rate was given for an age group, the mean value was substituted and the intake rate from the 6 to 11 age group was assumed to be the same for ages 7 to 11. There was no adjustment for preparation or cooking loss U.S. EPA 1998.

The soil migration to groundwater risk scenario is used to determine risk from groundwater exposure based on concentration in soil. Migration of contaminants from soil to groundwater can be envisioned as a two-stage process: (1) release of contaminant from soil to soil leachate and (2) transport of the contaminant through the underlying soil and aquifer to a receptor well. The soil to groundwater scenario considers both of these fate and transport mechanisms. The groundwater concentration is determined using a known concentration in soil, radionuclide specific Kd, and a dilution attenuation factor to obtain a risk. The soil to groundwater media option is included in both resident and indoor worker land use scenarios as they both model tapwater risk.

The user has the option to choose from two calculation methods. The first method employs the default partitioning equation for migration to groundwater. The dilution attenuation factor defaults to 20 for a 0.5-acre source. If the user has all of the parameters needed to calculate a dilution attenuation factor, you may use the Method 2 (mass-limit equation for migration to groundwater). The groundwater concentration, determined with either of these equations, is used to calculate the tapwater chronic daily intake equations presented in secion 4.1.4.

There are three parts of the above land use equations that require further explanation. The first is explanation of two inhalation variables: the particulate emission factor (PEF) and the volatilization factor (VF). The second is the use of the radionuclide decay constant (λ). The third is the explanation of the area correction factor (ACF).

Inhalation of isotopes adsorbed to respirable particles (PM10) was assessed using a default PEF equal to 1.36 x 109 m3/kg. This equation relates the contaminant concentration in soil with the concentration of respirable particles in the air due to fugitive dust emissions from contaminated soils. The generic PEF was derived using default values that correspond to a receptor point concentration of approximately 0.76 µg/m3. The relationship is derived by Cowherd (1985) for a rapid assessment procedure applicable to a typical hazardous waste site, where the surface contamination provides a relatively continuous and constant potential for emission over an extended period of time (e.g. years). This represents an annual average emission rate based on wind erosion that should be compared with chronic health criteria; it is not appropriate for evaluating the potential for more acute exposures. Definitions of the input variables are in Section 5.

With the exception of specific heavy metals, the PEF does not appear to significantly affect most soil screening levels. The equation forms the basis for deriving a generic PEF for the inhalation pathway. For more details regarding specific parameters used in the PEF model, refer to Soil Screening Guidance: Technical Background Document. The use of alternate values on a specific site should be justified and presented in an Administrative Record if considered in CERCLA remedy selection.

Note: the generic PEF evaluates wind-borne emissions and does not consider dust emissions from traffic or other forms of mechanical disturbance that could lead to greater emissions than assumed here.

EPA derived a default volatilization factor (VF) value of 17 m3/kg for tritium. The VF replaces the PEF in the risk equations when tritium is being addressed. This VF value is based on a steady-state model that assumes, on average, tritium in soil pore water and tritium in air (as tritiated water vapor) will be distributed in the environment in proportion to the average water content in soil and air. EPA assumes a mean atmospheric humidity of 6 grams of water per cubic meter of air (g/m3) nationwide (Etnier 1980) and an average soil moisture content of 10% (i.e., 100 grams of water per kilogram of soil). Given these assumptions, EPA calculates the VF term for tritium as

VFH-3 = 100 g H2O/kg soil ÷ 6 g H2O/m3 air

= 17 m3 air/kg soil

= 17 m3/kg

EPA believes that this value is appropriate for the average case, both outdoors and indoors. However, site managers can derive a site-specific VF term for tritium that may be more appropriate for a specific site, considering local atmospheric humidity and soil moisture content.

The equation to calculate the subchronic particulate emission factor (PEFsc) is significantly different from the residential and non-residential PEF equations. The PEFsc focuses exclusively on emissions from truck traffic on unpaved roads, which typically contribute the majority of dust emissions during construction. This equation requires estimates of parameters such as the number of days with at least 0.01 inches of rainfall, the mean vehicle weight, and the sum of fleet vehicle distance traveled during construction.

The number of days with at least 0.01 inches of rainfall can be estimated using Exhibit 5-2 in the supplemental soil screening guidance. Mean vehicle weight (W) can be estimated by assuming the numbers and weights of different types of vehicles. For example, assuming that the daily unpaved road traffic consists of 20 two-ton cars and 10 twenty-ton trucks, the mean vehicle weight would be:

The sum of the fleet vehicle kilometers traveled during construction (∑ VKT) can be estimated based on the size of the area of surface soil contamination, assuming the configuration of the unpaved road, and the amount of vehicle traffic on the road. For example, if the area of surface soil contamination is 0.5 acres (or 2,024 m2), and one assumes that this area is configured as a square with the unpaved road segment dividing the square evenly, the road length would be equal to the square root of 2,024 m2, 45 m (or 0.045 km). Assuming that each vehicle travels the length of the road once per day, 5 days per week for a total of 6 months, the total fleet vehicle kilometers traveled would be:

Other than emissions from unpaved road traffic, the construction worker may also be exposed to particulate matter emissions from wind erosion, excavation soil dumping, dozing, grading, and tilling or similar operations PEF'sc. These operations may occur separately or concurrently and the duration of each operation may be different. For these reasons, the total unit mass emitted from each operation is calculated separately and the sum is normalized over the entire area of contamination and over the entire time during which construction activities take place. Equation E-26 in the supplemental soil screening guidance was used.

The decay constant term (λ), which is based on the half-life of the isotope, is used for some media in nearly all land uses. λ = 0.693/half-life in years (where, 0.693=ln(2)). The term (1 - e-λt) takes into account the number of half-lives that will occur within the exposure duration to calculate an appropriate value. The intention of the +D term is to generate realistic risks by including the contributions from their short-lived decay products, assuming equal activity concentrations (i.e. , secular equilibrium) with the principal or parent nuclide in the environment. (Note that there is one exception to the assumption of secular equilibrium. For the inhalation slope factor for Rn-222+D reported in the table, EPA assumes a 50% equilibrium value for radon decay products (Po-218, Pb-214, Bi-214and Po-214) in air. ) In most cases, site-specific analytical data should be used to establish the actual degree of equilibrium between each parent radionuclide and its decay products in each media sampled. However, in the absence of empirical data, the "+D" values for radionuclides should be used unless there are compelling reasons not to do so. Definitions of the input variables are in Section 5.

The RAGS/HHEM Part B model assumes that an individual is exposed to a source geometry that is effectively an infinite slab. The concept of an infinite slab means that the thickness of the contaminated zone and its aerial extent are so large that it behaves as if it were infinite in its physical dimensions. In practice, soil contaminated to a depth greater than about 15 cm and with an aerial extent greater than about 1,000 m2 will create a radiation field comparable to that of an infinite slab. (U.S. EPA. 2000a)

To accommodate the fact that in most residential settings the assumption of an infinite slab source will result in overly conservative SSLs, an adjustment for source area is considered to be an important modification to the RAGS/HHEM Part B model. Thus, an area correction factor, ACF, has been added to the calculation of SSLs. (U.S. EPA. 2000a)

CDIs in this guidance are calculated without any shielding between them and the source (soil). In this case, a default soil gamma shielding factor for outdoor exposure to ionizing radiation (GSFo is established at 1.0 (0% shielding). It is common to have some shielding (soil cover) over contaminated soil. When the calculator is ran in site-specific mode the user must select a soil cover depth. Due to shielding, covering the contaminated area with soil will produce lower dose and risk coefficients that are stated in the Federal Guidance Report (FGR) 12 and 13. Therefore, gamma shielding factors are needed to apply the published EPA risk values to the buried contamination scenarios. Outdoor gamma shielding factors (GSFo) are derived by modeling various thicknesses of clean soil covering ground soil contamination. The gamma shielding factor is defined as the ratio of the dose corresponding to covered contamination to that of an unshielded surface source in soil. The MCNP output was used to derive kerma values one meter above the soil surface for various scenarios ranging from 0 cm soil cover to 100 cm soil cover in 10 cm increments while using source thicknesses of ground plane, 1, 5 and 15 cm source volumes as well as infinite source volume. Radioisotopes published in ICRP 107 were considered, along with decay chains of several radioisotopes. The Center for Radiation Protection Knowledge has provided GSFo values here and an appendix containing +D and +E values.

A default gamma shielding factor for indoor exposure to ionizing radiation (GSFi is established at 0.4 (60% shielding)

A default gamma shielding factor for exposure to ionizing radiation in air (GSFa is established at 1 (0% shielding)

The tables below present the definitions of the variables and their default values. This calculator follows the recommendations in the OSWER Directive concerning use of exposure parameters from the 2011 Exposure Factors Handbook. Any alternative values or assumptions used in remedy evaluation or selection on a CERCLA site should be presented with supporting rationale in Administrative Records.

NEC. Swine Nutrition Guide. Cooperative Extension Service / South Dakota State University and University of Nebraska / U.S. Department of Agriculture. Nebraska Cooperative Extension EC 95-273-C.

The pig water ingestion numbers are derived from the USDA "Swine Nutrition Guide" and the EPA Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities, found here. USDA assumes a pig consumes 1/4 to 1/3 gallons of water for every pound of dry feed. The midpoint of this range (7/24 gallons of water per 1 lbs. of dry feed) was used with the default dry feed, (4.7 kg) from the U.S. EPA, to come up with 3 gallons (11.4 L) per day default water intake.

NCRP 1996. Screening Models for Releases of Radionuclides to Atmosphere, Surface Water, and Ground, Vols. 1 and 2, NCRP Report No. 123. National Council on Radiation Protection and Measurements. http://www.ncrp.com/rpt123.html